Self-Lensing By Binaries

Lensing of one member of a binary by its companion is studied for several classes of binaries. For binaries in which at least one member is an ordinary (non-compact) star, the optical depths to lensing is extremely low, $\tau\lsim v_\esc^4/c^4\sim 10^{-11}$\mathrm{.}Here$v_\esc$ is the escape velocity from the component with the weaker potential. Binaries composed of two compact objects can have higher optical depths. About 0.2% of millisecond pulsar binaries will be self-lensing. Such objects can be used to probe the pulsar-emission mechanism.